The invention relates to acoustic ranging and, more particularly, to improved arrangements for close proximity ranging.
Acoustic ranging permits the determination of distance to a target without physical contact. Such systems typically operate in two successive cycles or modes. In the transmit mode, an ultrasonic pulse (an acoustic wave above about 20 kHz) is propagated toward a target at an unknown distance. In the receive mode, the reflected sound energy or echo from the target is detected. The time between the generation of the transmit pulse and receipt of the echo is proportional to the target range.
The SX-70 brand cameras made by Polaroid Corporation, Cambridge, Mass., are an example of commercial products which incorporate ultrasonic ranging. The Polaroid ranging device comprises a capacitive transducer which doubles as a transmitter and receiver. This dual-function design is advantageously compact and economical.
In prior dual-function transducer systems, accurate ranging is limited to a minimum distance of about 1 foot. This is largely due to the time required for the transducer and associated driving circuitry to return to a quiescent state after the transmit cycle. There are many promising applications for ultrasonic ranging, however, in which it is desirable to accurately measure much shorter distances. In the field of robotics, for example, shortrange sensors have useful potential for feedback control.
It is therefore an object of the invention to provide an acoustic arrangement for close proximity ranging.